Kazuyoshi Moriya

Tropical warming and intermittent cooling during the Cenomanian/Turonian oceanic anoxic event 2: Sea surface temperature records from the equatorial Atlantic

Oceanic anoxic event 2 (OAE-2) occurring during the Cenomanian/Turonian (C/T) transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 Myr. However, the impact of this major perturbation on and interaction with global climate remains unclear. Here we report new high-resolution records of sea surface temperature (SST) based on TEX86 and ?18O of excellently preserved planktic foraminifera and stable organic carbon isotopes across the C/T transition from black shales located offshore Suriname/French Guiana (Demerara Rise, Ocean Drilling Program Leg 207 Site 1260) and offshore Senegal (Cape Verde Basin, Deep Sea Drilling Project Leg 41 Site 367). At Site 1260, where both SST proxy records can be determined, a good match between conservative SST estimates from TEX86 and ?18O is observed. We find that late Cenomanian SSTs in the equatorial Atlantic Ocean (?33°C) were substantially warmer than today (~27°–29°C) and that the onset of OAE-2 coincided with a rapid shift to an even warmer (~35°–36°C) regime. Within the early stages of the OAE a marked (~4°C) cooling to temperatures lower than pre-OAE conditions is observed. However, well before the termination of OAE-2 the warm regime was reestablished and persisted into the Turonian. Our findings corroborate the view that the C/T transition represents the onset of the interval of peak Cretaceous warmth. More importantly, they are consistent with the hypotheses that mid-Cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide (CO2) and that major OAEs were capable of triggering global cooling through the negative feedback effect of organic carbon-burial-led CO2 sequestration. Evidently, however, the factors that gave rise to the observed shift to a warmer climate regime at the onset of OAE-2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 Myr.

Testing for ice sheets during the mid-Cretaceous greenhouse using glassy foraminiferal calcite from the mid-Cenomanian tropics on Demerara Rise

The mid-Cretaceous is widely considered the archetypal ice-free greenhouse interval in Earth history, with a thermal maximum around Cenomanian-Turonian boundary time (ca. 90 Ma). However, contemporaneous glaciations have been hypothesized based on sequence stratigraphic evidence for rapid sea-level oscillation and oxygen isotope excursions in records generated from carbonates of questionable preservation and/or of low resolution. We present new oxygen isotope records for the mid-Cenomanian Demerara Rise that are of much higher resolution than previously available, taken from both planktic and benthic foraminifers, and utilizing only extremely well preserved glassy foraminifers. Our records show no evidence of glaciation, calling into question the hypothesized ice sheets and rendering the origin of inferred rapid sea-level oscillations enigmatic. Simple mass-balance calculations demonstrate that this Cretaceous sea-level paradox is unlikely to be explained by hidden ice sheets existing below the limit of δ 18 O detection.

Demersal habitat of Late Cretaceous ammonoids: Evidence from oxygen isotopes for the Campanian (Late Cretaceous) northwestern Pacific thermal structure

Comparison of oxygen isotope data for exceptionally well preserved cooccurring plankton and benthos from the Campanian of Hokkaido, Japan, with nine species of ammonoids clearly indicates the demersal (nektobenthic) habitat of ammonoids; unlike Nautilus , the ammonoids studied did not engage in significant short-term vertical migrations in the water column. The new foraminiferal isotopic data suggest that sea-surface and sea-bottom temperatures were ∼26 and 18 °C, respectively, at 40°N in the Campanian northwestern Pacific. The temperatures were significantly warmer than those in the modern northwest Pacific. This finding provides the first reliable evidence for the warm Late Cretaceous mid-latitude North Pacific. Isotopic analyses of ammonoids show that the average calcification temperature of all ammonoid shells analyzed was ∼19 °C, comparable to those of cooccurring benthos. None of these ammonoids display calcification temperatures equivalent to those of planktonic foraminifers.

Planktonic foraminiferal zonation in the Cretaceous Yezo Group, Central Hokkaido, Japan

Abstract The mudstone of the Yezo Group exposed in Central Hokkaido yields abundant microfossils of calcareous nannofossils, foraminifers, radiolarians and dinoflagellates. Benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence, while specimens of planktonic foraminifers are generally fewer than benthics in all samples. We recognized the following 13 planktonic foraminiferal zones assigned to the late Aptian to early Campanian in the Oyubari and Haboro–Kotanbetsu areas; (1) Globigerinelloides spp., (2) Ticinella primula , (3) Biticinella breggiensis , (4) Rotalipora subicinensis – Rotalipora ticinensis , (5) Rotalipora appenninica , (6) Rotalipora globotruncanoides , (7) Rotalipora cushmani (8), Whiteinella archaeocretacea (9) Helvetoglobotruncana helvetica , (10) Marginotruncana pseudolinneiana , (11) Marginotruncana sinuosa , (12) Contusotruncana fornicata , (13) Globotruncana arca . The Globigerinelloides spp. to H. helvetica Zones (late Aptian to early Turonian) can be correlated with standard zones in the Tethyan regions, whereas the assemblages from the M. pseudolinneiana to G. arca zones lack tropical zonal markers of Dicarinella concavata , D. asymetrica and Globotruncanita elevata in many studied sections. The scarcity or lack of tropical zonal species during the late Turonian to early Campanian suggests that the Oyubari and Haboro–Kotanbetsu regions in Hokkaido were located in the Transitional to Boreal biogeographical provinces.

Prevailing oxic environments in the Pacific Ocean during the mid-Cretaceous Oceanic Anoxic Event 2

The occurrence of Oceanic Anoxic Event 2 (OAE2) 94 million years ago is considered to be one of the largest carbon cycle perturbations in the Earths history. The marked increase in the spatial extent of the anoxic conditions in the worlds oceans associated with OAE2 resulted in the mass accumulation of organic-rich sediments. Although extensive oceanographic studies of OAE2 have been undertaken in the Atlantic Ocean, the Tethys Sea, and the epicontinental seas of Europe and America, little is known about OAE2 in the Pacific Ocean. Here, we present high-resolution carbon-isotope and degree of pyritization (DOP) data from marine sequences that formed along the continental margins of North America and Asia below the northeastern and northwestern Pacific Ocean. The predominance of low DOP values in these areas revealed that the continental margins of the Pacific Ocean were oxic for most of the OAE2 interval.

Fault model of the 2007 Noto Hanto earthquake estimated from coseismic deformation obtained by the distribution of littoral organisms and GPS: Implication for neotectonics in the northwestern Noto Peninsula

We investigate the coseismic vertical crustal movement along the northern and western coast of the Noto Peninsula caused by the Noto Hanto earthquake on March 25, 2007, from the distribution of supra-, mid- and infra-littoral organisms. The highest uplift of 44 cm is observed at Akakami and the maximum subsidence of 8 cm at Fukami. We construct a rectangular fault model with a uniform slip in elastic half-space using both the coseismic vertical displacement estimated from the distribution of these organisms and the coseismic crustal deformation obtained by GPS. The model shows a reverse fault with a right-lateral slip of 1.3 m in a 18.6 km×14.5 km area. The seismic moment is 1.0×1019 N m (MW 6.6) using a rigidity of 30 GPa. The geometry of the source fault is consistent with the distribution of aftershocks and active faults, and the fault is restricted to the central area of the aftershock area. Relationships among the fault, the distribution of aftershocks, active faults, and geological blocks around the source area suggest that geological structures restrict the fault size of the earthquake. By considering an inclined altitudinal distribution of marine terraces and the coseismic vertical crustal deformation detected in this study, we estimate that the recurrence of earthquakes during the past 120 kyr would produce a vertical crustal deformation of ≈12 m and the background tectonic uplift would reach ≈28 m.

Phospholipid-Derived Fatty Acids and Quinones as Markers for Bacterial Biomass and Community Structure in Marine Sediments

Phospholipid-derived fatty acids (PLFA) and respiratory quinones (RQ) are microbial compounds that have been utilized as biomarkers to quantify bacterial biomass and to characterize microbial community structure in sediments, waters, and soils. While PLFAs have been widely used as quantitative bacterial biomarkers in marine sediments, applications of quinone analysis in marine sediments are very limited. In this study, we investigated the relation between both groups of bacterial biomarkers in a broad range of marine sediments from the intertidal zone to the deep sea. We found a good log-log correlation between concentrations of bacterial PLFA and RQ over several orders of magnitude. This relationship is probably due to metabolic variation in quinone concentrations in bacterial cells in different environments, whereas PLFA concentrations are relatively stable under different conditions. We also found a good agreement in the community structure classifications based on the bacterial PLFAs and RQs. These results strengthen the application of both compounds as quantitative bacterial biomarkers. Moreover, the bacterial PLFA- and RQ profiles revealed a comparable dissimilarity pattern of the sampled sediments, but with a higher level of dissimilarity for the RQs. This means that the quinone method has a higher resolution for resolving differences in bacterial community composition. Combining PLFA and quinone analysis as a complementary method is a good strategy to yield higher resolving power in bacterial community structure.

Development of the cretaceous greenhouse climate and the oceanic thermal structure

Abstract. The development of the climate during the Cretaceous greenhouse interval is reviewed based on geological and paleontological records, geochemical proxy records for paleotemperature and atmospheric carbon-dioxide concentration (pCO2), the production rate of oceanic crust, and the timing and scale of emplacement of large igneous provinces. Geological and paleontological evidence, and paleotemperature records indicate that the Early Cretaceous climate was relatively cool, possibly accompanied by the development of continental ice sheets. Subsequent warming reached a peak in the Turonian, when sea surface temperatures in equatorial and high-latitude regions exceeded 36° C and 20° C, respectively. The possibility of a maximum temperature above 36° C at the equator is inconsistent with the cirrus cloud negative-feedback hypothesis proposed for the modern ocean, which may indicate that the hypothesis is not valid for an ice-free greenhouse system. Although elevated levels of pCO2 are thought to be responsible for this extreme warming, the timing of the pCO2 maxima differs from the timing of oceanic volcanic activity, which emitted massive amounts of CO2 into the atmosphere, by ∼30 m.y.: volcanic activity peaked at ∼120 Ma, whereas pCO2, temperature, and sea-level peaked at ~90 Ma, indicating that the abiotic Mesozoic marine revolution was not a simple, single event. Moreover, the occurrence of intermittent cooling during the Late Cretaceous, coupled with sea-ice development in the Arctic Ocean, suggests that the mid-Cretaceous greenhouse system was capable of producing not only extreme warmth but also seasonal freezing. Although the Mesozoic marine revolution is assumed to have been triggered by the general warming that occurred during the Cretaceous, a more precise analysis of the timing and magnitude of biotic events is required to understand the paleoecosystem of this greenhouse period.

Isotope Signature of Ammonoid Shells

Geochemical analyses of ammonoid shells provide an independent and objective data set to evaluate life and habitat of the animal. This uniformitarian consideration, in combination with functional morphology and physical evidence for ecology or physiology, potentially delivers a significant advantage for new insights in paleoecology. One difficulty is that ammonoids as a proxy carrier are assumed to be mobile organisms. In contrast to stationary proxy carriers like benthic bivalves, it is difficult to impossible to estimate absolute depth or locality in which a certain proxy was recorded. Although the temperature proxy is very informative, it could indicate alternative scenarios; shallower calcification depth or calcification in the warmer season. When the calcification temperature is calibrated against the thermal structure of the water column, the proxy records would be fully understood. Therefore, providing the external frame of references is significantly important for getting better insights from geochemical signatures on ammonoids.

Late Maastrichtian carbon isotope stratigraphy and cyclostratigraphy of the Newfoundland Margin (Site U1403, IODP Leg 342)

Earth’s climate during the Maastrichtian (latest Cretaceous) was punctuated by brief warming and cooling episodes, accompanied by perturbations of the global carbon cycle. Superimposed on a long-term cooling trend, the middle Maastrichtian is characterized by deep-sea warming and relatively high values of stable carbon-isotope ratios, followed by strong climatic variability towards the end of the Cretaceous. A lack of knowledge on the timing of climatic change inhibits our understanding of underlying causal mechanisms. We present an integrated stratigraphy from Integrated Ocean Drilling Program (IODP) Site U1403, providing an expanded deep ocean record from the North Atlantic (Expedition 342, Newfoundland Margin). Distinct sedimentary cyclicity suggests that orbital forcing played a major role in depositional processes, which is confirmed by statistical analyses of high resolution elemental data obtained by X-ray fluorescence (XRF) core scanning. Astronomical calibration reveals that the investigated interval encompasses seven 405-kyr cycles (Ma4051 to Ma4057) and spans the 2.8 Myr directly preceding the Cretaceous/Paleocene (K/Pg) boundary.